Electrode Assembly

ABSTRACT

An electrode assembly includes a plurality of electrodes arranged in a stack along a stacking axis, where each of the electrodes is separated from a successive one of the electrodes in the stack by a respective planar portion of an elongated separator sheet. The elongated separator sheet may be folded between each planar portion such that the elongated separator sheet follows a serpentine path traversing back and forth orthogonal to the stacking axis to extend between each successive one of the electrodes in the stack. First lateral ends of a plurality of electrodes may be offset by a first distance in the orthogonal dimension with respect to the first lateral end of either the first electrode in the stack or one of the two adjacent electrodes in the stack, where the first distance is no more than 10% of a lateral width of any select one of the electrodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Korean Patent Application No. 10-2021-0090589 filed on Jul. 9, 2021, Korean Patent Application No. 10-2021-0090588 filed on Jul. 09, 2021, Korean Patent Application No. 10-2021-0090590 filed on Jul. 9, 2021, Korean Patent Application No. 10-2021-0090591 filed on Jul. 9, 2021, Korean Patent Application No. 10-2021-0090592 filed on Jul. 9, 2021, Korean Patent Application No. 10-2021-0090596 filed on Jul. 9, 2021, Korean Patent Application No. 10-2021-0090597 filed on Jul. 9, 2021, Korean Patent Application No. 10-2021-0090598 filed on Jul. 9, 2021, Korean Patent Application No. 10-2021-0090600 filed on Jul. 9, 2021, and Korean Patent Application No. 10-2021-0090601 filed on Jul. 9, 2021, the entire contents of all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an electrode assembly. In particular, the present invention relates to an electrode assembly of a secondary battery.

BACKGROUND ART

Secondary batteries, unlike primary batteries, are rechargeable, and have been widely researched and developed in recent years due to their small size and large capacity. As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing.

Secondary batteries can be classified into a coin-type battery, a cylindrical battery, a prismatic battery, and a pouch-type battery, according to the shape of the battery case. In a secondary battery, an electrode assembly mounted inside a battery case is a chargeable/dischargeable power generating element having a stacked structure comprising electrodes and separators.

The electrode assembly may be generally classified into a jelly-roll type, a stack type, and a stack-and-folding type. In the jelly-roll type, a separator is interposed between a sheet type positive electrode and a sheet type negative electrode, each of which are coated with an active material, and the entire arrangement is wound. In the stack type, a plurality of positive and negative electrodes are sequentially stacked with a separator interposed therebetween. In a stack-and-folding type, stacked unit cells are wound with a long-length separation film.

In a stack-and-folding type electrode assembly in the related art, the electrodes and the separator stacked in the electrode assembly are bonded to each other by applying heat and pressure to the assembled stack. However, the electrode assemblies of the related art have problems in that the electrodes in the stack can become misaligned during that application of heat and pressure.

SUMMARY OF THE INVENTION

The present invention provides, among other things, an electrode assembly having increased density of electrodes and increased energy density, by minimizing the degree to which stacked electrodes within the electrode assembly are shifted laterally with respect to the stacking direction of the electrode assembly.

An exemplary aspect of the present invention provides an electrode assembly. The electrode assembly in accordance with such aspect of the invention preferably includes a plurality of electrodes arranged in a stack along a stacking axis, where each of the electrodes in the stack is separated along the stacking axis from a successive one of the electrodes in the stack by a respective planar portion of an elongated separator sheet. The elongated separator sheet may be folded between each planar portion such that the elongated separator sheet follows a serpentine path traversing back and forth along an orthogonal dimension orthogonal to the stacking axis to extend between each successive one of the electrodes in the stack. Each of the electrodes in the stack may have a first lateral end and a second lateral end on opposite sides of the respective electrode in the orthogonal dimension. The first lateral ends of a plurality of electrodes may be offset by a first distance in the orthogonal dimension with respect to the first lateral end of either the first electrode in the stack or one of the two adjacent electrodes in the stack. That first distance is preferably no more than 10% of a lateral width of any select one of the electrodes, where the lateral width is defined between the first and second lateral ends of the select electrode.

In accordance with another exemplary aspect of the present invention, an electrode assembly is provided. The electrode assembly accordance with such aspect of the invention preferably includes a plurality of electrodes arranged in a stack along a stacking axis, where each of the electrodes in the stack is separated along the stacking axis from a successive one of the electrodes in the stack by a respective planar portion of an elongated separator sheet. The elongated separator may be folded between each planar portion such that the elongated separator sheet follows a serpentine path traversing back and forth along an orthogonal dimension orthogonal to the stacking axis to extend between each of successive one of the electrodes in the stack. Each of the electrodes in the stack may have a first lateral end and a second lateral end on opposite sides of the respective electrode in the orthogonal dimension. The first lateral ends of more than one of the plurality of electrodes are preferably aligned along a line extending parallel to the stacking axis.

In accordance with another exemplary aspect of the present invention, an electrode assembly is provided. The electrode assembly accordance with such aspect of the invention preferably includes a plurality of electrodes arranged in a stack along a stacking axis, where each of the electrodes in the stack is separated along the stacking axis from a successive one of the electrodes in the stack by a respective planar portion of an elongated separator sheet. The elongated separator may be folded between each planar portion such that the elongated separator sheet follows a serpentine path traversing back and forth along an orthogonal dimension orthogonal to the stacking axis to extend between each of successive one of the electrodes in the stack. The stacking axis of the stack may connect a centroid of each of multiple ones of the electrodes in the stack. Moreover, a centroid of at least one of the plurality of electrodes may be offset by a first distance in the orthogonal dimension with respect to the stacking axis. Preferably, the first distance is no more than 10% of a lateral width of any select one of the electrodes, where the lateral width is defined between first and second lateral ends of the respective electrode on opposite sides of the select electrode in the orthogonal dimension.

According to the present invention, the electrodes are desirably aligned and fixed so that the positions of the electrodes are not misaligned, energy density is improved, and it is possible to prevent the electrode from protruding towards the exterior of a battery containing the electrode assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating an electrode assembly according to an exemplary embodiment of the present invention.

FIG. 2 is a perspective view conceptually illustrating the stacking of components of an electrode assembly according to an exemplary embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating electrode assemblies according to exemplary embodiments of the present invention.

FIG. 4 is a cross-sectional view illustrating electrode assemblies according to other exemplary embodiments of the present invention.

FIG. 5 is a cross-sectional view illustrating an electrode assembly according to still another exemplary embodiment of the present invention.

FIG. 6 is a cross-sectional view illustrating an electrode assembly according to yet another exemplary embodiment of the present invention.

FIG. 7 is a cross-sectional view illustrating electrode assemblies according to still yet other exemplary embodiments of the present invention.

FIG. 8 is a cross-sectional view of the electrode assembly of FIG. 1 , illustrating positions of an upper surface, a lower surface, and a middle portion of the electrode assembly.

FIG. 9 is a top plan view illustrating an electrode assembly manufacturing apparatus for manufacturing the electrode assembly according to the present invention.

FIG. 10 is a front elevation view conceptually illustrating the electrode assembly manufacturing apparatus of FIG. 9 .

FIG. 11 is a perspective view of a separator heating unit of a separator supply unit according to the exemplary embodiment of the present invention.

FIG. 12A is a perspective view illustrating a first press unit according to the exemplary embodiment of the present invention, and FIG. 12B is a perspective view illustrating a second press unit according to the exemplary embodiment of the present invention.

DETAILED DESCRIPTION

The detailed description of the present invention is intended to completely explain the present invention to those skilled in the art. Throughout the specification, when it is said that a part “includes” a certain element or that a specific structure or shape is “characterized,” this does not mean, unless otherwise noted, that other components or other structures are excluded. Rather, other components, structures and shapes may indeed be included.

Since the present invention may be variously transformed and may have various exemplary embodiments, specific exemplary embodiments are presented and described in detail in the detailed description. However, this is not intended to limit the scope of the invention, which should be understood to include all transformations, equivalents, and substitutes consistent with the spirit and scope of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings. However, the drawings are for illustrating the present invention, and the scope of the present invention is not limited by the drawings.

FIG. 1 is a cross-sectional view illustrating an electrode assembly 10 according to an exemplary embodiment of the present invention, and FIG. 2 is a perspective view illustrating the stacking of electrodes 1, 2 and a separator 4 into a stack S of the electrode assembly 10 according to an exemplary embodiment of the present invention.

The electrode assembly 10 according to the present invention is a chargeable/dischargeable power generating device, and may include a stack S in which electrodes are disposed between portions of an elongated separator 4 that is folded in a zigzag manner such that the separator 4 follows a serpentine profile extending between each of the electrodes along the stacking direction Y. In this case, the electrodes may include one or more first electrodes 1 and one or more second electrodes 2 alternating with one another along the stacking direction Y.

The serpentine profile of the separator 4 along the stacking direction Y may be defined by successive folded portions P of the separator 4, such that each folded portion P of the separator 4 wraps around one end 6 of an electrode in the lateral dimension Z (orthogonal to the stacking direction Y) before the separator 4 passes between that electrode and the next adjacent electrode in the stack S while extending to the opposing lateral side of the stack S. The portions of the separator 4 extending between each electrode in the stack S may be referred to as stacking portions of the separator 4. Thus, each level of the stack S (defined by the position of each electrode along the stack S) may be characterized by a folded portion P of the separator 4 surrounding the lateral end 6 of the electrode on one side of the electrode in the lateral dimension Z, while the opposite side of the electrode along the lateral dimension Z may be defined by an open region O characterized by the absence of the separator 4 (including any folded portion P). The folded portions P, like the open regions on the opposite side of the stack S, may thus alternate their positions on opposing lateral sides of the stack S for each successive level of the stack.

As discussed further herein, an “upper surface” of the electrode assembly 10 refers to the uppermost position of the electrode assembly 10 in the stacking direction of the electrode assembly, which is designated by reference numeral 12 in FIG. 8 . Further, as discussed herein, a “lower surface” of the electrode assembly 10 refers to the lowermost position of the electrode assembly 10 in the stacking direction of the electrode assembly, which is designated by reference numeral 13 in FIG. 8 . Finally, as discussed herein, the “middle” of the electrode assembly 10 refers to a middle position between the upper surface and the lower surface of the electrode assembly 10 in the stacking direction of the electrode assembly, as designated by reference numeral 11 in FIG. 8 . For example, when an electrode assembly 10 formed of nine electrodes and viewed from the side, as in FIG. 8 , the “middle” position relates to the position of the fifth electrode in the stack S. Thus, subsequent references to “middle air permeability” relate to air permeability of the separator 4 abutting the middle electrode in the electrode assembly. Likewise, subsequent references to “middle adhesive force” refer the adhesive force between the middle electrode in the electrode assembly and the abutting portion of the separator 4.

Referring to FIGS. 9 and 10 , an apparatus 100 for manufacturing an electrode assembly according to an exemplary embodiment of the present invention includes a stack table 110; a separator supply unit 120 for supplying a separator 4 from a separator roll 122; a first electrode supply unit 130 for supplying a first electrode 1; a second electrode supply unit 140 for supplying a second electrode 2; a first electrode stack unit 150 for stacking the first electrode 1 on the stack table 110; a second electrode stack unit 160 for stacking the second electrode 2 on the stack table 110; and a press unit 180 for bonding the first electrode 1, the separator 4, and the second electrode 2 to each other. Further, the apparatus 100 for manufacturing the electrode assembly according to the exemplary embodiment of the present invention may include a holding mechanism 170 for fixing the stack S (comprising the first electrode(s) 1, the second electrode(s) 2, and the separator 4) to the stack table 110 as the stack S is being assembled.

The separator supply unit 120 may have a passage through which the separator 14 passes towards the stack table 110. In particular, the separator supply unit 120 may include a separator heating unit 121 defining the passage through which the separator 14 passes towards the stack table 110. As shown in FIG. 11 , the separator heating unit 121 may include a pair of bodies 121 a, each of which may be in the form of a square block, and the bodies 121 a may be spaced apart by a distance defining one of the dimensions of the passage through which the separator 14 passes. At least one or both of the bodies 121 a may further include a separator heater 121 b for heating the respective body 121 a, and thereby transferring heat to the separator 14.

The separator supply unit 120 may further include a separator roll 122 on which the separator 14 is wound. Thus, the separator 14 wound on the separator roll 122 may be gradually unwound and pass through the formed passage to be supplied to the stack table 110.

The first electrode supply unit 130 may include a first electrode roll 133 on which the first electrode 1 is wound in the form of a sheet, a first cutter 134 for cutting the first electrode 1 at regular intervals to form the first electrodes 1 having a predetermined size when the first electrode 1 is unwound and supplied from the first electrode roll 133, a first conveyor belt 135 for moving the first electrode 1 cut by the first cutter 134, and a first electrode supply head 136 for picking up (e.g., via vacuum suction) the first electrode 1 transferred by the first conveyor belt 135 and seating the first electrode 1 on a first electrode seating table 131.

The second electrode supply unit 140 may include a second electrode seating table 141 on which the second electrode 2 is seated before being stacked on the stack table 110 by the second electrode stack unit 160. The second electrode supply unit 140 may further include a second electrode roll 143 on which the second electrode 2 is wound in the form of a sheet, a second cutter 144 for cutting the second electrode 2 at regular intervals to form the second electrode 2 of a predetermined size when the second electrode 2 is unwound and supplied from the second electrode roll 143, a second conveyor belt 145 for moving the second electrode 121 cut by the second cutter 144, and a second electrode supply head 146 for picking up (e.g., via vacuum suction) the second electrode 2 transferred by the second conveyor belt 145 and seating the second electrode on the second electrode seating table 141.

The first electrode stack unit 150 may be structured to stack the first electrode 1 on the stack table 110. The first electrode stack unit 150 may include a first suction head 151 and a first moving unit 153. The first suction head 151 may pick up the first electrode 1 seated on the first electrode seating table 131 via vacuum suction through one or more vacuum suction ports (not shown) formed on a bottom surface of the first suction head 150, and then the first moving unit 153 may move the first suction head 151 to the stack table 110 so as to allow the first suction head 151 to stack the first electrode 1 on the stack table 110.

The second electrode stack unit 160 may also be structured to stack the second electrode 2 on the stack table 110. The second electrode stack unit 160 may have the same structure as that of the foregoing first electrode stack unit 150. In such case, the second electrode stack unit 160 may include a second suction head 161 and a second moving unit 163. The second suction head 161 may pick up the second electrode 2 seated on the second electrode seating table 141 via vacuum suction. The second moving unit 163 may then move the second suction head 161 to the stack table 110 so as to allow the second suction head 161 to stack the second electrode 2 on the stack table 110.

The stack table 110 may be rotatable so as to rotate between positions facing the first electrode stack unit 150 and the second electrode stack unit 160. As the stack table 110 rotates, the holding mechanism 170 may hold the stack being assembled (comprising the first electrode 1, the second electrode 2, and the separator 4) in order to secure the position of the stack relative to the stack table 110. For example, the holding mechanism 170 may apply downward pressure to the upper surface of the stack to press it towards the stack table 110. The holding mechanism 170 may include, for example, a first holder 171 and a second holder 172 to fix opposing sides of the first electrode 1 or the second electrode 2. The holders 171, 172 may each be in the form of one or more clamps or other clamping mechanisms.

Thus, in operation, the first electrode 11 is supplied from the first electrode supply unit 130 to the first electrode stack unit 150, the first electrode stack unit 150 stacks the first electrode 11 on the upper surface of the separator 14 stacked on the stack table 110. The holding mechanism 170 then presses down on the upper surface of the first electrode 11 to secure the position of the first electrode 11 on the stack table 110. Thereafter, the stack table 110 is rotated in the direction of the second electrode stack unit 160 while the separator 14 is continuously supplied so as to cover the upper surface of the first electrode 11. Meanwhile, the second electrode 12 is supplied from the second electrode supply unit 140 and is stacked by the second electrode stack unit 160 on a portion of the separator 14 where the separator 14 covers the upper surface of the first electrode 11. Then the holding mechanism 170 releases the upper surface of the first electrode 11 and then presses down on the upper surface of the second electrode 12 to secure the position of the stack S being built vis-a-vis the stack table 110. Thereafter, by repeating the process of stacking the first electrode 11 and the second electrode 12, the stack S in which the separator 14 is zig-zag-folded and positioned between each of the successive first and second electrodes 11, 12 may be formed.

After the components of the electrode assembly are stacked, the electrode assembly may undergo one or more heat press operations. In particular, the electrode assembly may be moved to the press unit 180, which applies heat and pressure to the stack S by advancing heated pressing blocks 181 and 182 towards one another with the stack S positioned therebetween. As a result, the components of the stack S (i.e., the electrodes and separator) are thermally bonded to one another, so as to desirably prevent the completed electrode assembly from falling apart or the components of the electrode assembly from shifting their positions within the stack S.

The heat press operations applied to the electrode assembly may include a primary heat press operation and a secondary heat press operation. The primary heat press relates to an operation after the first electrode(s) and the second electrode(s) are alternately stacked between the folded separators to define a stack S, where the stack S is gripped with a gripper 51, and then the stack S is heated and pressed. The secondary heat press operation relates to an operation after the primary heat press operation, in which the gripping of the stack S by the gripper 51 is ceased and the stack S is once more heated and pressed.

The method may first include a stack process of assembling a stack (stack cell) on a stack table by alternately stacking the first electrode and the second electrode on the separator, where the separator is continuously supplied and sequentially folded over a previously-stacked one of the first and second electrodes before a subsequent one of the first and second electrodes is stacked. After the stack process, the stack may be moved away from the stack table. During such time, the separator is pulled, and, after the separator is pulled for a predetermined length, the separator is cut. Thereafter, the predetermined length of he cut end of the separator is wound around the stack cell. The movement of the stack away from the stack table may be accomplished by the gripper 51, which is desirably a movable component that can grip the stack on the stack table 110 and then move the stack to the press unit 180, where the heat press operations are performed. The primary heat press operation is then performed in a state in which the wound stack cell is gripped with the gripper 51. After the primary heat press operation is completed, the grip of the stack cell by the gripper 51 is released. After the gripper 51 is removed, the secondary heat press operation is performed. When the secondary heat press operation is completed, the finished electrode assembly may be complete.

The press unit 180 may be divided into a first press unit 50 and a second press unit 60, where the first press unit 50 can be used for the primary heat press operation (or pre-heating), and the second press unit 60 can be used for the secondary heat press operation.

Referring to FIGS. 12A and 12B, the first press unit 50 may primarily heat and press the stack S in a fixed state. The first press unit 50 includes a pair of first pressing blocks 50 a and 50 b and may further include the gripper 51 configured for fixing the stack S. In fixing the stack S, the gripper 51 may hold the stack S by pressing the upper and lower surfaces of the stack S towards one another along the stacking direction (along the y axis) to fix the relative positions of the first electrodes 11, the second electrodes 12, and the separator 14. As in the example shown, to hold these relative positions, the gripper 51 may press the upper and lower surfaces of the stack S.

The pair of first pressing blocks 50 a and 50 b of the first press unit 50 may move in directions towards and away from each other. In moving towards each other, the pair of first pressing blocks 50 a and 50 b may compress either one or both of the stack S and the gripper 51.

In this manner, the first press unit 50 may heat and compress the stack S to reduce or eliminate any spaces between the first electrodes 11, the separator 14, and the second electrodes 12 included in the stack S, so as to bond such components of the stack S together.

As shown, each pressing surface of the pair of first pressing blocks 50 a and 50 b configured for contact with and compression of the stack S may define planes. At least one of the pair of first pressing blocks 50 a and 50 b may include a gripper groove 52 having a shape corresponding to a fixing part 51 b of the gripper 51 described further herein. In the example shown in FIG. 12A, each of the pair of first pressing blocks 50 a and 50 b include four gripper grooves 52 to correspond with four fixing parts 51 b. However, there may be a greater or fewer number of gripper grooves 52. Preferably, the number of gripper grooves 52 should match the number of fixing parts to be used.

The gripper 51 may include a main body 51 a and a plurality of fixing parts 51 b. As in the arrangement shown, the main body 51 a may have a length along an x axis and a height along a y axis that are the same or approximately the same as the length and height of the stack S along those respective axes. In some other arrangements, the main body may be longer than the length of the stack S in the x axis and have a greater height than the height of the stack S in the y axis. The fixing parts 51 b preferably may be in the form of a rod, column, or plate that extend along a width direction (z axis) of the stack S. Here, the length of the stack S in the x axis may refer to the portion of the stack having the longest distance from one end to the other end of the stack S, and the height in the y axis may refer to the distance in the stacking direction of the stack S, and the width in the z axis may refer to a distance in a direction perpendicular to both the x and y axes.

The fixing parts 51 b may be provided in two rows in which one row is adjacent to a pressing surface of pressing block 50 a while the other row is adjacent to a pressing surface of pressing block 50 b. The position of each of the fixing parts 51 b may be adjustable in the height direction of the main body 51 a. In this manner, each of the fixing parts 51 b may be placed in contact with, and preferably along the width of, the upper and lower surfaces of the stack S to fix the position of the stack S and the relative positions of the first electrode 11 and the second electrode 12 within the stack S.

In some arrangements, the second press unit 60 may heat and compress the stack S that was previously heated and compressed by the first press unit 50, so as to secondarily compress the already primarily compressed stack S.

As shown in FIG. 12B, the second press unit 60 includes a pair of second pressing blocks 60 a and 60 b. The pair of pressing blocks 60 a and 60 b may be moved in directions towards and away from each other. In moving towards each other, the pair of pressing blocks 60 a and 60 b may press upon the upper and lower surfaces of the stack S to compress the stack.

As shown, each pressing surface of the pair of second pressing blocks 60 a and 60 b configured for contact with and compression of the stack S may define planes. As in the example shown, in some arrangements, grooves for the fixing parts 51 b may be excluded from the second pressing blocks 60 a and 60 b. In some other arrangements, at least one of the pair of second pressing blocks 60 a and 60 b may include one or more grooves having a shape corresponding to the fixing part 51 b of the gripper 51.

In some arrangements, each of the pair of first pressing blocks 50 a and 50 b of the first press unit 50 include gripper grooves 52 having a shape corresponding to the fixing part 51 b of the gripper 51, and each of the pair of second pressing blocks 60 a and 60 b of the second press unit 60 have flat pressing surfaces without any gripper grooves.

In some arrangements, the second press unit 60 may heat and press only a portion of the stack S on which the gripper 51 is (or was previously) located, which were not heated and pressed by the first press unit 50. In some other arrangements, the second press unit 50 may heat and press the entire upper and lower surfaces of the stack.

In some arrangements, the first press unit 50 may compress the heated stack S initially and with the upper surface and the lower surface of the stack S fixed with the gripper 51 to reduce or eliminate the spaces between, while bonding, the first electrodes 11, the separator 14, and the second electrodes 2 included in the stack S, so as to bond such components of the stack S together in the regions of the stack S in which the gripper 51 is not located.

In some such arrangements, the second press unit 60 may compress and heat the stack S which has already been preliminarily bonded by the first press unit 50, and from which the gripper 51 has been removed. The second press unit 60 may thus reduce or eliminate any spaces between the first electrodes 11, the separator 4, and the second electrodes 12 included in the stack S, so as to bond such components of the stack S together in the regions of the stack S in which the gripper 51 previously pressed the stack S during the initial pressing operation by the first press unit 50. In some such arrangements, each of the pair of second pressing blocks 60 a and 60 b may be a quadrangular block in the form of a rectangular parallelepiped. In such arrangements, the pair of second pressing blocks 60 a and 60 b may have the flat pressing surfaces described previously herein.

In some arrangements, each of the pair of first pressing blocks 50 a and 50 b of the first press unit 50 may have the flat pressing surfaces. In some such arrangements, each of the pair of second pressing blocks 60 a and 60 b of the second press unit 60 may have grooves having the shape corresponding to the fixing parts 51 b of the gripper 51.

In some arrangements, the fixing part 51 b may include a heat-conducting material, such as a thermally conductive metal material selected from the group consisting of aluminum and iron. By conducting heat to the stack S, when the first press unit 50 compresses the stack S fixed by the gripper 51, the electrodes 11, 12, and separator 4 may be bonded together as the spaces between them are reduced or eliminated.

In some arrangements, the second press unit 60 may not compress regions of the stack S on which the gripper 51 was previously located, but may instead only compress regions of the stack S where the gripper was not previously located and upon which the press unit 50 did not press during the initial pressing.

Further, each of the pair of first pressing blocks 50 a and 50 b may be a quadrangular block in the form of a rectangular parallelepiped. In such arrangements, the pair of first pressing blocks 50 a and 50 b may have the flat pressing surfaces described previously herein.

Either one or both of the first and second press units 50 and 60 preferably include a press heater (not illustrated), configured for heating the respective pair of first and second pressing blocks 50 a, 50 b, 60 a, and 60 b such that the blocks may heat the stack S when pressing upon the stack. In this manner, when the stack S is pressed with the first and second press units 50 and 60, thermal fusion between the first electrodes 11, the separator 14, and the second electrodes 12 may be better achieved such that stronger bond may be formed among these layers.

In any one or more of the pairs of first and second pressing blocks 50 a, 50 b, 60 a, and 60 b, both the length and the width of the respective pressing surfaces may be greater than the corresponding length and width (in the x and z axes, respectively) of the stack S.

As noted above, the assembly of the electrode assembly 10 may be completed by bonding the first and second electrodes 1,2 to the separator 4 by applying heat and pressure to the stack S. For example, by pressing opposing surfaces of the stack S using a press unit (which may include a pair of heated press blocks configured to advance towards one another with the stack S positioned therebetween) such bonding may be achieved by thermal fusion. The opposing surfaces of the stack S pressed by the press unit may be the upper surface and the lower surface of the stack S on opposite sides of the stack in the stacking direction Y.

The electrode assembly 10 may be provided in a form in which an outer circumference thereof is surrounded by an outer separator 5, which may be a portion (e.g., a tail end) of the same elongated separator 4 that follows the zigzag or serpentine profile along the stack S, as discussed above. In one example, the outer circumference of the electrode assembly 10 surrounded by the outer separator 5 is the upper surface and the lower surface in the stacking direction Y, as well as at least one pair of opposing side surfaces in the lateral dimension Z. Here, the upper surface of the stack S may mean the outer surface forming the upper side of the stack S in the stacking direction Y, and the lower surface may mean the outer surface forming the lower side of the stack S, opposite to the upper surface. Thus, when the stack S is pressed by the heated press unit, an inner side of the outer separator 5 surrounding the outermost portion of the stack S may be bonded to the adjacent portions of serpentine separator 4 (i.e., folded portions P), as well as to the lateral ends 6 of the first and second electrodes 1, 2 in the lateral dimension Z that are exposed to the adjacent outer separator 5 by the open regions characterized by the absence of folded portions P.

Accordingly, by bonding the components of the electrode assembly 10 together in this way, unfolding of the stack S may be prevented and battery stability may be improved. In addition, there may be no need for a separate adhesive tape or tool for preventing the unfolding of the stack S, which may shorten manufacturing time lead to increased process efficiency.

In some arrangements of the present invention, the positive electrode may be manufactured by, for example, coating a positive electrode current collector with a positive electrode coating mixture comprising a positive electrode active material, a conductive material, and a binder and then drying the coating mixture. If necessary, a filler may be added to the mixture. Such materials may be any appropriate materials used in the relevant field, in particular those commonly used for the particular application.

For example, the positive electrode active material may include: layered compounds, such as lithium cobalt oxide (LiCoO₂) and lithium nickel oxide (LiNiO₂), or compounds substituted with one or more transition metals; lithium manganese oxides represented by the chemical formula Li_(1+x)Mn_(2−x)O₄ (where x is 0 to 0.33), such as LiMnO₃, LiMn₂O₃, and LiMnO₂; lithium copper oxide (Li₂CuO₂); vanadium oxides, such as LiV₃O₈, LiFe₃O₄, V₂O₅, and Cu₂V₂O₇; Nickel (Ni) site-type lithium nickel oxide represented by the chemical formula LiN_(1−x)M_(x)O₂ (wherein M=Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x=0.01 to 0.3); lithium manganese composite oxides represented by the chemical formula LiMn_(2−x)M_(x)O₂ (where M=Co, Ni, Fe, Cr, Zn or Ta, and x=0.01 to 0.1) or Li₂Mn₃MO₈ (where M=Fe, Co, Ni, Cu, or Zn); LiMn₂O₄ in which a part of Li in the formula is substituted with an alkaline earth metal ion; disulfide compounds; and Fe₂(MoO₄)₃, but the present invention is not limited to such materials.

The materials that may be used for the positive electrode current collector is not particularly limited. The positive electrode current collector preferably has a relatively high conductivity without causing a chemical change when used in a battery. For example, stainless steel; aluminum; nickel; titanium; calcined carbon; or a material in which a surface of aluminum or stainless steel is treated with carbon, nickel, titanium, silver, and the like may be used. Preferably, the positive electrode current collector may be aluminum. Adhesion between the current collector and the positive electrode coating mixture desirably may be increased by including fine irregularities on a surface of the current collector interfacing with the coating mixture. Moreover, various structural configurations of the positive electrode current collector may be used, such as a film, a sheet, a foil, a net, a porous body, a foam body, and a non-woven body. The positive electrode current collector generally may have a thickness in a range from 3 μm to 500 μm.

the conductive material in the positive electrode coating mixture generally may be included in an amount from 1 to 50 wt % of the total weight of the mixture including the positive electrode active material. The conductive material is not particularly limited and preferably has conductivity without causing a chemical change when used in a battery. For example, graphite, such as natural graphite and artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers, such as carbon fibers and metal fibers; carbon and metal powders, such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives, may be used for the conductive material.

The binder in the positive electrode coating mixture assists in bonding between the active material and the conductive material in bonding the coating mixture to the current collector. Such binder is generally included in an amount from 1 to 50% by weight of the total weight of the mixture including the positive electrode active material. Examples of the binder may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluororubber, and various copolymers.

The filler optionally added to the positive electrode coating mixture may be used as a component to suppress the expansion of the positive electrode. Such a filler is not particularly limited and may include a fibrous material that does not cause a chemical change when used in a battery. For example, olefin polymers, such as polyethylene and a polypropylene, and fibrous materials, such as glass fiber and carbon fiber, may be used.

In some arrangements, the negative electrode may be manufactured by coating, drying, and pressing a negative electrode active material on a negative electrode current collector, and, if necessary, the conductive materials, binders, fillers, and the like discussed above may be optionally further included. In any event, any appropriate materials used in the relevant field may be used, in particular those commonly used for the particular application. For example, as the negative electrode active material, carbon, such as non-graphitizable carbon and graphitic carbon; metal composite oxide represented by the chemical formulas LixFe₂O₃(0≤x≤1), Li_(x)WO₂(0≤x≤1), Sn_(x)Me_(1−x)Me′yOz (Me: Mn, Fe, Pb, Ge; Me′: Al, B, P, Si, elements of groups 1, 2 and 3 of the periodic table, and halogens; 0<x≤1; 1≤y≤3; 1≤z≤8); lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; metal oxides, such as SnO, SnO₂, PbO, PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄, and Bi₂O₅; conductive polymers, such as polyacetylene; and Li—Co—Ni-based materials may be used.

The materials that may be used for the negative electrode current collector are not particularly limited. The negative electrode current collector preferably has high conductivity without causing a chemical change in the battery. For example, copper; stainless steel; aluminum; nickel; titanium; calcined carbon; a material in which a surface of copper or stainless steel is surface-treated with carbon, nickel, titanium, silver, and the like; and an aluminum-cadmium alloy may be used.

In addition, like the positive electrode current collector, the bond between the negative electrode current collector and the negative electrode active material may be strengthened by forming fine irregularities on the surface of the positive electrode current collector. Various structural configurations of the negative electrode current collector may also be used, such as a film, a sheet, a foil, a net, a porous body, a foam body, a non-woven body, and the like. In addition, the negative electrode current collector may have a thickness generally in a range of 3 μm to 500 μm.

In some arrangements, the separator may be an organic/inorganic complex porous SRS (Safety-Reinforcing Separator). The SRS may have a structure in which a coating layer component including inorganic particles and a binder polymer is coated on a polyolefin-based separator substrate.

Since the SRS does not undergo high-temperature thermal contraction due to the heat resistance of the component inorganic particles, even if the electrode assembly is penetrated by a needle-shaped conductor, an elongated length of the safety separator can be maintained.

The SRS may have a uniform porous structure formed by an interstitial volume between the inorganic particles that are components of the coating layer, in addition to the porous structure of the separator substrate itself. The pores may not only significantly alleviate any external impacts applied to the electrode assembly, but may also facilitate the movement of lithium ions through the pores, as well as enable a large amount of electrolyte to be impregnated into the separator, thereby promoting improved performance of the battery.

In some arrangements, the separator may be dimensioned in its width dimension (orthogonal to the longitudinal dimension in which the separator is unrolled) such that separator portions extend outwardly on both sides beyond corresponding edges of adjacent positive and negative electrodes (hereinafter “surplus portions”). Moreover, such outwardly extending portions of the separator may have a structure including a coating layer thicker than a thickness of the separator formed on one or both sides of the separator in order to prevent shrinkage of the separator. For more information regarding the thicker coating layer on the outwardly extending surplus portions of the separator, see Korean Patent Application Publication No. 10-2016-0054219, the entire contents of which are incorporated herein by reference. In some arrangements, each separator surplus portion may have a size of 5% to 12% of the width of the separator. Moreover, in some arrangements, the coating layer may be coated on both surfaces of the separator over a width of 50% to 90% of the width of each separator surplus portion. In addition, the widths of the coating layers may be the same or different on each surface of the separator. In some arrangements, the coating layer may include inorganic particles and a binder polymer as components.

In exemplary embodiments of the present invention, examples of the polyolefin-based separator component may include high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, or derivatives thereof.

In some arrangements, the thickness of the coating layer may be smaller than the thickness of the first electrode or the second electrode. In some such arrangements, the thickness of the coating layer may be 30% to 99% of the thickness of the first electrode or the second electrode.

In some arrangements, the coating layer may be formed by wet coating or dry coating.

In some arrangements, the polyolefin-based separator substrate and the coating layer may exist in a form in which pores on the surface of the substrate and the coating layer are anchored with each other, whereby the separator substrate and the coating layer may be bonded together firmly.

The substrate and the coating layer of the separator may have a thickness ratio from 9:1 to 1:9. A preferred thickness ratio may be 5:5.

In some arrangements, the inorganic particles may be inorganic particles commonly used in the art. The inorganic particles may interact with each other to form micropores in the form of empty spaces between the inorganic particles while structurally helping to maintain the physical shape of the coating layer. In addition, since the inorganic particles generally have properties that do not change their physical properties even at high temperatures of 200° C. or more, the resultant organic/inorganic complex porous film generally and desirably has excellent heat resistance.

In addition, the materials that may be used for the inorganic particles are not particularly limited but are preferably electrochemically stable. That is, the inorganic particles are preferably selected such that oxidation and/or reduction reactions do not occur in the operating voltage range of the applied battery (for example, 0 to 5 V based on Li/Li+). In particular, the use of inorganic particles having ion transport ability may improve performance by increasing the ionic conductivity in the electrochemical device. Thus, use of inorganic particles having ionic conductivity as high as possible is preferable. In addition, when the inorganic particles have a high density, it is difficult to disperse the inorganic particles during coating, and it can also undesirably increase the weight of the battery. Therefore, use of inorganic particles having density as low as possible is preferable. In addition, inorganic materials having a high dielectric constant contribute to an increase in the degree of dissociation of electrolyte salt, such as a lithium salt, in a liquid electrolyte, thereby improving the ionic conductivity of the electrolyte.

For the above reasons, the inorganic particles may be at least one type selected from the group consisting of inorganic particles having piezoelectricity and inorganic particles having lithium ion transport ability.

Inorganic particles having piezoelectricity refer to materials which are a nonconductor at normal pressure, but have a property of conducting electricity due to a change in the internal structure when a certain pressure is applied. They are also materials which exhibit high permittivity characteristics with a permittivity constant of 100 or more. Inorganic particles having piezoelectricity also generate an electric potential difference between opposing surfaces, e.g., of a separator, by causing one surface to be positively charged and the other surface to be negatively charged, or vice versa, when either tension or compression is applied to an object composed of the inorganic particles, e.g., a separator.

When the inorganic particles having the above characteristics are used as a coating layer component, in the case of an internal short circuit of both electrodes due to an external impact, such as by a needle-shaped conductor, the positive electrode and the negative electrode may not directly contact one another due to the inorganic particles coated on the separator. Moreover, due to the piezoelectricity of the inorganic particles, an electric potential difference may occur within the particles, which desirably may result in electron movement between both electrodes (i.e., the flow of a minute current), so that it may be possible to gently reduce the voltage of the battery, thereby improving safety.

Examples of materials for the inorganic particles having piezoelectricity may be one or more selected from the group consisting of BaTiO₃, Pb(Zr,Ti)O₃ (PZT), those represented by the chemical formula Pb_(1−x)La_(x)Zr_(1−y)Ti_(y)O₃ (PLZT), PB(Mg₃Nb_(2/3))O₃—PbTiO₃ (PMN-PT), and hafnia (HfO₂), but are not limited to these materials.

Inorganic particles having lithium-ion transport ability refer to inorganic particles containing a lithium element but not storing lithium and instead having a function of moving lithium ions. The inorganic particles having lithium-ion transport ability are capable of transporting and moving lithium ions due to a kind of defect in the particle structure. As a result, the lithium-ion conductivity in the battery may be improved, thereby improving battery performance.

Examples of materials for the inorganic particles having lithium-ion transport ability may be one or more selected from the group consisting of lithium phosphate (Li₃PO₄), lithium titanium phosphate (represented by the chemical formula Li_(x)Ti_(y)(PO₄)₃, wherein 0<x<2, 0<y<3), lithium aluminum titanium phosphate (represented by the chemical formula Li_(x)Al_(y)Ti_(z)(PO₄)₃, wherein 0<x<2, 0<y<1, 0<z<3), glass of the series represented by the chemical formula (LiAlTiP)_(x)O_(y) (0<x<4, 0<y<13), lithium lanthanum titanate (represented by the chemical formula Li_(x)La_(y)TiO₃, wherein 0<x<2, 0<y<3), lithium germanium thiophosphate (represented by the chemical formula Li_(x)Ge_(y)P_(z)S_(w), wherein 0<x<4, 0<y<1, 0<z<1, 0<w<5), lithium nitride (represented by the chemical formula Li_(x)N_(y), wherein 0<x<4, 0<y<2), glass of the SiS₂ series (represented by the chemical formula Li_(x)Si_(y)S_(z), wherein 0<x<3, 0<y<2, 0<z<4), and glass of the P₂S₅ series (represented by the chemical formula Li_(x)P_(y)S_(z), wherein 0<x<3, 0<y<3, 0<z<7), but are not limited to these materials.

The composition ratio of the inorganic particles and the binder polymer, which are components of the coating layer of the separator, is not particularly limited, but may be adjusted within the range of 10:90 to 99:1 by weight %, and preferably within the range of 80:20 to 99:1 by weight %. When the composition ratio is less than 10:90 by weight %, the content of the polymer may become excessively large, and the pore size and porosity may be reduced due to a decrease in the empty space formed between the inorganic particles, finally resulting in deterioration of the battery performance. On the other hand, when the composition ratio exceeds 99:1 by weight %, the content of the polymer may be too small, and the mechanical properties of the final organic/inorganic composite porous separator may be deteriorated due to weakened adhesive force between the inorganic materials.

In some arrangements, a binder polymer commonly used in the art may be used as the binder polymer.

The coating layer of the organic/inorganic composite porous separator may further include other commonly known additives in addition to the aforementioned inorganic particles and binder polymer.

In some arrangements, the coating layer may be referred to as an active layer.

The present invention beneficially minimizes shifting of the electrodes during application of heat and pressure to the assembled stack to bond the electrodes and separator to one another. In particular, one or more electrodes may shift in the lateral dimension Z from the intended position (which may be a position in which the centroid of the electrode is disposed along the central stacking axis of the stack S). As a result, with reference to FIGS. 3-6 , an undesirable overhang h may be created. That overhang h represents a dimension in the lateral direction Z by which any of the first and second electrodes 1, 2 is displaced laterally due to the electrode having shifted in the lateral dimension Z from the intended position. Such overhang h may be defined as the distance along the lateral dimension Z by which the lateral end 6 of one electrode is displaced out of alignment with respect to the lateral end 6 of an adjacent one of the electrodes.

In the electrode assembly 10 of the present invention, an overhang h may be minimized or omitted entirely by gripping the stack S with a gripper 51 during at least an initial heating and pressing process for bonding the components of the electrode assembly 10.

In the electrode assembly 10 according to the present invention, n electrodes are stacked (n is an integer equal to or greater than 2), and the lateral end 6 of at least one of the m^(th) electrodes (m is an integer from 2 to n) stacked among the electrodes may protrude in the lateral dimension Z (i.e., towards the folded portion P of the separator 4 or towards the opposite, open region O) by an amount h relative to the lateral end 6 of the first, m−1^(th) stacked electrode, or the m+1^(th) stacked electrode, where the value of h is 10% or less of the width of the electrode in the lateral dimension Z. As used herein, “protrude(s)” refers to displacement of the lateral end 6 of one electrode out of alignment (along a line parallel to the stacking direction Y) with the lateral end 6 of another electrode, whether the lateral end 6 of the subject electrode projects outwardly or is recessed inwardly relative to the other electrode.

In the electrode assembly 10, the lateral end 6 of at least one electrode may protrude laterally relative to the lateral end 6 of the first electrode, the electrode stacked immediately below, or the electrode stacked immediately above, and a maximum of n electrodes may protrude in that manner.

The electrodes in the electrode assembly 10 may include one or more first electrodes 1 and one or more second electrodes 2. When the first electrodes 1 are negative electrodes, the second electrodes 2 are positive electrodes. Conversely, if the first electrodes 1 are positive electrodes, the second electrodes 2 are negative electrodes.

For example, when n is 10 (i.e., there are 10 electrodes in the electrode assembly 10), there will be five first electrodes 1 and five second electrodes 2 stacked (in the order of: first electrode 1, then separator 4, then second electrode 2, and so on). In addition, a lateral end 6 of the fourth stacked second electrode 2 may protrude laterally relative to the third stacked first electrode 1 or the fifth stacked first electrode 1.

In one example, all of the side ends of the five first electrodes 1 may be positioned along the same line parallel to the stacking direction Y of the electrode assembly 10, and the remaining second electrodes 2 (except for the fourth stacked second electrode 2) may also be positioned on the same line. That is, in the electrode assembly 10, only the fourth stacked second electrode 2 may protrude.

FIG. 3 is a cross-sectional view illustrating an electrode assembly 10 according to an exemplary embodiment of the present invention. In the stack S according to the exemplary embodiment, the lateral end 6 of the m^(th) stacked electrode (m is an integer from 2 to n) among the electrodes may protrude relative to the lateral end 6 of the m−1^(th) stacked electrode or the m+1^(th) stacked electrode in the lateral dimension Z by 10% or less of the electrode width. For example, when n is 4, the lateral end 6 of the second stacked second electrode 2 may protrude relative to the lateral end 6 of the first or third stacked first electrodes 1; the lateral end 6 of the third stacked first electrode 1 may protrude relative to the lateral end 6 of the second or fourth stacked second electrode 2, and the lateral end 6 of the fourth stacked second electrode 2 may protrude from the lateral end 6 of the third stacked first electrode 1.

(a) of FIG. 3 a cross-sectional view illustrating an electrode assembly 10 when the electrodes protrude only towards the folded portion P of the separator 4, and (b) of FIG. 3 is a cross-sectional view illustrating an electrode assembly 10 when the electrodes protrude both towards the folded portion P and towards open region O. That is, (b) of FIG. 3 is a cross-sectional view illustrating the electrode assembly 10 in which the second stacked second electrode 2 protrudes towards the folded portion P, the third stacked first electrode 1 protrudes towards the open region O, and the fourth stacked second electrode 2 protrudes towards the folded portion P.

FIG. 4 is a cross-sectional view illustrating an electrode assembly 10 according to another exemplary embodiment of the present invention. In the electrode assembly 10, the lateral end 6 of the m^(th) stacked electrode (m is an integer from 2 to n) may protrude relative to the lateral end 6 of the first stacked electrode towards the folded portion P or towards the open region O by 10% or less of the electrode width.

For example:

(a) of FIG. 4 is a cross-sectional view of an electrode assembly 10 in which the remaining electrodes except for the first stacked electrode protrude towards the folded portion P. (b) of FIG. 4 is a cross-sectional view of an electrode assembly 10 in which the remaining electrodes except for the first stacked electrode protrude alternately towards the folded portion P and towards the open region O.

Referring to (b) of FIG. 4 , the lateral ends 6 of the second to fourth stacked electrodes protrude in one direction from the lateral end 6 of the first stacked electrode, but the second and fourth stacked electrodes may be positioned so that one lateral end 6 of each of the electrodes is on the same line along a direction parallel to the stacking direction.

FIG. 5 is a cross-sectional view illustrating an electrode assembly 10 according to still another exemplary embodiment of the present invention. In the electrode assembly 10, the lateral ends 6 of first electrodes 1 and second electrodes 2 are aligned so as to be positioned on the same line along a direction parallel to the stacking direction of the electrode assembly 10, and the other electrodes that are not so aligned may be considered to protrude relative to the lateral ends 6 of the aligned electrodes.

For example, when n is 10, the side ends of the first, third, fifth, seventh, and ninth stacked first electrodes 1 may be positioned on the same line along the direction parallel to the stacking direction, and the lateral ends 6 of the second, fourth, sixth, eighth, and tenth stacked second electrodes 2 may protrude relative to the lateral ends 6 of the first, third, fifth, seventh, and ninth stacked first electrodes 1.

FIG. 6 is a cross-sectional view illustrating an electrode assembly 10 according to yet another exemplary embodiment of the present invention. In the electrode assembly 10, the lateral end 6 of the m^(th) stacked electrode (m is an integer from 2 to n) may protrude from the lateral end 6 of the m−2^(th) stacked electrode or the m+2^(th) stacked electrode towards the folded portion P or towards the open region 0.

For example, when n is 6, although the first stacked first electrode 1 and the second stacked second electrode 2 do display an overhang h, such electrodes may nevertheless be considered to be aligned because their centroids are located on the same line along the direction parallel to the stacking direction of the electrode assembly 10.

Further, the lateral end 6 of the third stacked first electrode 1 may protrude relative to the lateral end of the first stacked first electrode 1, and the lateral end 6 of the fourth stacked second electrode 2 may protrude relative to the lateral end 6 of the second stacked second electrode 2. That is, the same electrodes may be a reference for protrusion, and the protruding length or the overhang h may increase in the stacking direction of the electrode assembly 10.

FIG. 7 is a cross-sectional view illustrating an electrode assembly 10 according to still yet another exemplary embodiment of the present invention. In the electrode assembly 10, the lateral ends 6 of the electrodes may be positioned on the same line in a direction parallel to the stacking direction of the stack.

(a) of FIG. 7 is a cross-sectional view of an electrode assembly 10 when the widths of the first electrodes 1 and the second electrodes 2 are different, and (b) of FIG. 7 is a cross-sectional view of the electrode assembly 10 when the widths of the first electrodes 1 and the second electrodes 2 are the same.

For example, when n is 10, the lateral ends 6 of the first, third, fifth, seventh, and ninth stacked first electrodes 1 may be located on the same line along a direction parallel to the stacking direction, and the lateral ends 6 of the second, fourth, sixth, eighth, and tenth stacked second electrodes 2 may be located on the same line along a direction parallel to the stacking direction.

In this case, at least one side surface of the lateral ends 6 of the first electrodes 1 and the second electrodes 2 may be located on the same line, or both side surfaces may not be located on the same line.

In the electrode assembly 10 according to the present invention, the protruding length of the electrode protruding from the side end may be 10% or less of the width of any one of the first electrode 1 and the second electrode. Preferably, the protruding length of the electrode protruding from the side end may be 1% to 10% of the width of any one of the first electrode 1 and the second electrode.

The first electrode 1 and the second electrode 2 may have the same width or different widths. In exemplary embodiments, when the first electrodes 1 are negative electrodes and the second electrodes 2 are positive electrodes, the lateral width of the positive electrodes may be larger than the lateral width of the negative electrodes, or the lateral width of the positive electrodes and the negative electrode may be the same, or the lateral width of the positive electrodes may be smaller than the lateral width of the negative electrodes.

In the electrode assembly 10 according to the present invention, the protruding length of the m^(th) stacked electrode may be 10% or less of the width of the electrode having a larger width.

Alternatively, the protruding length of the m^(th) stacked electrode may be 0.1 mm to 10 mm.

When the protruding length satisfies the above numerical range, the degree of protrusion of the electrode protruding from the side end of the electrode assembly 10 may be minimized so as to increase the electrode and energy density.

As used herein, “adhesive force” refers to the adhesive force between the first electrode 1 and the separator or between the second electrode 2 and the separator. In accordance with the present invention, a method for measuring adhesive force of the separator is not particularly limited. In accordance with one measurement method, samples having a width of 55 mm and a length of 20 mm are each adhered to a respective slide glass with the electrode being positioned on the adhesive surface of the slide glass. The samples are then each tested by performing a 90° peel test at a speed of 100 mm/min pursuant to the testing method set forth in ASTM-D6862. That is, an edge of the separator is pulled upwardly at 90° relative to the slide glass at a speed of 100 mm/min so as to peel the separator away from the electrode along the width direction of the sample (i.e., peeling from 0 mm to 55 mm). Utilizing such testing method, the adhesive force between the electrodes and the separator in the electrode assembly 10 may have a value in range from 5 gf/20 mm to 65 gf/20 mm. Preferably, the adhesive force between the first electrode 1 and the separator 4 may be in a range from 20 gf/20 mm to 65 gf/20 mm, and the adhesive force between the second electrode 2 and the separator 4 may be in a range from 5 gf/20 mm to 15 gf/20 mm.

When the adhesive force of the electrode assembly 10 is less than 5 gf/mm, the adhesive force of the electrode assembly 10 may be considered low, and thus a problem may occur when the electrode assembly 10 is moved during the manufacturing process. That is, the components of the assembled stack S may separate and fall apart from one another.

On the other hand, when the adhesive force of the electrode assembly 10 exceeds 65 gf/mm, air permeability and electrolyte wetting ability of the separator are reduced, such that it is difficult for the electrolyte to penetrate into the electrode assembly 10, thereby decreasing the initial capacitance and increasing the initial resistance value.

The air permeability of the separators 4 according to the exemplary embodiment and other exemplary embodiments of the present invention may have a value in a range from 70 sec/ml to 95 sec/ml.

In the present invention, the method for measuring the air permeability of the separator is not particularly limited. In the method utilized and discussed further herein, the air permeability was measured by using a method commonly used in the art, namely, according to the JIS Gurley measurement method of the Japanese industrial standard using a Gurley type Densometer (No. 158) manufactured by Toyoseiki. That is, the air permeability of the separator was obtained by measuring the time it takes for 100 ml (or 100 cc) of air to pass through the separator of 1 square inch under a pressure of 0.05 MPa at room temperature (i.e., 20° C. to 25° C.).

When the air permeability of the separator 4 is less than 70 sec/ml, the wetting performance of the electrolyte is low and the movement path of ions may be blocked, thereby reducing the performance of the electrode assembly 10. On the other hand, when the air permeability of the separator 4 exceeds 95 sec/ml, the adhesive force of the first electrode 1 and the second electrode 2 may be reduced, which leads to shifting of the electrodes (i.e., increase of the overhang h) in the electrode assembly 10.

1) EXAMPLE 1

19 positive electrode sheets, 20 negative electrode sheets, and an elongated separator were supplied to the stack table from the respective positive electrode supply unit, negative electrode supply unit, and separator supply unit.

More specifically, the positive electrode and the negative electrode were supplied after being cut from a positive electrode sheet and a negative electrode sheet, respectively, and the separator was supplied in the form of an elongated separator sheet. Thereafter, the supplied separator was folded while rotating the stack table and stacking the positive electrodes and the negative electrode as described above. A gripper was used to press down on and stabilize the stack, which resulted in a stack including 39 electrodes.

After assembling the stack, a primary heat press operation was performed by gripping the stack with the gripper and pressing for 15 seconds while heating the stack under a temperature condition of 70° C. and a pressure condition of 1.91 MPa.

After the primary heat press operation, the gripper was released from the stack and the secondary heat press operation was performed, in which the pressing block was heated to a temperature of 70° C. (temperature condition), and a pressure of 2.71 Mpa (pressure condition) was applied to the stack with the pressing block for 10 seconds (press time), thus resulting in the electrode assembly of Example 1.

In the process of manufacturing the electrode assembly, the above-described disclosure of the present invention may be applied.

2) EXAMPLES 2 TO 12

Electrode assemblies of Examples 2 to 12 were manufactured in the same manner as in Example 1, except that the secondary heat press operation was performed under the temperature conditions, pressure conditions, and press time represented in Table 1 below in Example 1. That is, the primary heat press conditions of Examples 1 to 12 are the same.

TABLE 1 Primary heat press Temperature Pressure condition condition Press area (314.57 cm²) Press time (° C.) Tonf MPa (s) Example 1 70 6 1.91 15 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12 Secondary heat press Temperature Pressure condition Press condition Press area (554.1 cm²) time (° C.) Tonf MPa (s) Example 1 70 5 2.71 10 Example 2 70 5 2.71 20 Example3 70 4 2.17 10 Example4 70 4 2.17 20 Example 5 60 4 2.17 10 Example 6 60 4 2.17 20 Example 7 60 5 2.71 10 Example 8 60 5 2.71 20 Example 9 80 4 2.17 10 Example 10 80 4 2.17 20 Example 11 80 5 2.71 10 Example 12 80 5 2.71 20

3) COMPARATIVE EXAMPLES 1 TO 5

Electrode assemblies of Comparative Examples 1 to 5 were manufactured in the same manner as in Example 1, except that the primary heat press operation was performed under the temperature conditions, pressure conditions, and press time represented in Table 2 below, and the secondary heat press operation was not performed.

TABLE 2 Primary heat press Temperature Pressure condition Press condition Press area (314.57 cm²) time (° C.) Tonf MPa (s) Comparative 70 6 1.91 8 Example 1 Comparative 80 6 1.91 8 Example 2 Comparative 90 4 1.27 8 Example 3 Comparative 90 4 1.27 15 Example 4 Comparative 90 6 1.91 8 Example 5 Comparative 90 8 2.54 8 Example 6 Comparative 90 8 2.54 15 Example 7 Temperature Pressure condition Press condition Press area (554.1 cm²) time (° C.) Tonf MPa (s) Comparative — — — — Example 1 Comparative — — — — Example 2 Comparative — — — — Example 3 Comparative — — — — Example 4 Comparative — — — — Example 5 Comparative — — — — Example 6 Comparative — — — — Example 7

All of the electrode assemblies of Examples 1 to 12 and Comparative Examples 1 to 5 manufactured under the conditions of Tables 1 and 2 were tested by picking each of them up with a vacuum suction mechanism under the same conditions as the electrode supply unit discussed above, and the vacuum suction mechanism attempted to hold the electrode assemblies for 60 sections. In all the electrode assemblies of Comparative Examples 1 to 5, it was observed that the electrodes and separator became separated before 60 seconds. That means that the electrode assemblies of Comparative Examples 1 to 5 had poor adhesion between the electrode and the separator, whereas the electrode assembly according to the present application (which was subjected to the primary and the secondary press operations), had a good adhesion state, and thus had the excellent effect of preventing the resisting any unfolding and falling apart of the electrode assembly.

In the case of Comparative Examples 6 and 7, although the electrodes and separator were not observed to separate before 60 seconds, it was confirmed that damage to the electrode assembly occurred. This is believed to have occurred because the first press was performed under a pressure condition of 2.54 Mpa (high pressure).

4) EXPERIMENTAL EXAMPLE 1— ADHESIVE FORCE EVALUATION AND WITHSTAND VOLTAGE EVALUATION

Adhesive forces between surfaces at the upper end, the lower end, and the middle of the stack S were measured by disassembling (i.e., separating the layers of) the electrode assemblies of Examples 1 to 12 and Comparative Examples 6 and 7 (in which the separation of the electrodes and separator were not observed before 60 seconds in the previous test) and then analyzing the separated layers. Specifically, adhesive force between the negative electrode and the separator located at the lowermost end of the stack was measured. Additionally, adhesive force between the negative electrode and the separator located at the uppermost end of the stack was measured. Finally, adhesive force between the negative electrode and the separator located at a middle location along the stacking direction of the stack was measured.

In each of the separated electrode assemblies, the negative electrode and the separator sampled had a width of 55 mm and a length of 20 mm. The sampled sample was adhered to the slide glass with the electrode being positioned on the adhesive surface of the slide glass. After that, the slide glass with the sample was mounted to the adhesive force measuring device and tested by performing 90° peel test at a speed of 100 mm/min pursuant to the testing method set forth in ASTM-D6862, as discussed above. After discounting any initial significant fluctuations, the values for applied force per sample width (in grams/mm) were measured while the separator was peeled away from the electrode.

The results are represented in Table 3 below.

TABLE 3 Negative electrode adhesive force (gf/20 mm) Upper Lower surface Middle surface deviation Example 1 19.8 10.8 21.5 10.7 Example 2 20.3 9.7 19.5 10.6 Example 3 9.9 5.2 11.4 6.2 Example 4 16.6 9.2 17 7.8 Example 5 9.4 4.0 9.9 5.9 Example 6 11.1 7.1 14.3 7.2 Example 7 7.9 6.2 10.5 4.3 Example 8 13.4 8.9 18 9.1 Example 9 14 5.2 10.4 8.8 Example 10 14.2 7.9 14.6 6.7 Example 11 16.7 7.2 18.5 11.3 Example 12 25.3 12.0 22.4 13.3 Comparative 15.6 7.2 25.9 18.7 Example 6 Comparative 30.7 12.6 25.1 18.1 Example 7

In addition, the withstand voltages of the electrode assemblies of Examples 1, 6 and 12 and Comparative Examples 1 to 7 were also measured.

The results are represented in Table 4 below.

TABLE 4 Withstand voltage (kV) Example 1 1.58 Example 6 1.56 Example 12 1.58 Comparative Example 1 1.82 Comparative Example 2 1.51 Comparative Example 3 1.49 Comparative Example 4 1.47 Comparative Example 5 1.48 Comparative Example 6 1.45 Comparative Example 7 1.45

Investigating the results of Table 4, it was confirmed that the adhesive force of Examples 1 to 3 was superior to that of Comparative Example 1, in which only the primary heat press operation was performed under conditions similar to those of the Examples.

In addition, investigating the results of Table 6, it was confirmed that the withstand voltage of Examples 1 to 3, in which the primary heat press operation was performed under higher temperature and higher pressure conditions than those of the Comparative Examples had a range of 1.56 kV or more and 1.8 kV or less.

That is, the electrode assembly of the present invention has excellent adhesive force and at the same time, has a withstand voltage suitable for use as an electrode assembly. In that regard, a withstand voltage of 1.8 kV or less was confirmed.

It is believed that this is because the electrode assembly was manufactured by the manufacturing method including both the primary and secondary heat press.

5) EXPERIMENTAL 2—EVALUATION OF AIR PERMEABILITY

Among Examples 1 to 12, the air permeability of the electrode assemblies of Examples 1, 6, and 12, which differed only in the temperature condition of the secondary press, was evaluated.

Specifically, after collecting the separators in the electrode assemblies of Examples 1, 6, and 12, the separators were cut to prepare separator samples having a size of 5 cm×5 cm (width X length). After that, the separator samples were washed with acetone.

Air permeability of Examples 1, 6, and 12 were measured by measuring the time it took for 100 ml (or 100 cc) of air to pass through the separator of 1 square inch at room temperature and under the pressure condition of 0.05 MPa by using a Gurley type Densometer (No. 158) from Toyoseiki in accordance with the JIS Gurley measurement method of the Japanese industrial standard.

The results are represented in Table 5.

TABLE 5 Air permeability Upper Lower surface Middle surface Deviation Example 1 88 76 84 11.1 Example 6 88 75 87 12.3 Example 12 101 84 100 17.4 Comparative 76 74 77 3.0 Example 1

From the results of Table 5, when the condition of the secondary heat press operation according to the present invention is satisfied, it was confirmed that the air permeability corresponding to each location was less than 120 sec/100 ml, although they had an appropriate level of air permeability for use as an electrode assembly. It was also confirmed that the deviations in air permeability between each location were also less than 20 sec/100 ml, which was considered to be substantially uniform. That is, it was confirmed once again that the electrode assembly manufactured by the manufacturing method according to the present invention had uniform performance.

In addition, it was confirmed that the air permeability deviation between each location was less than 20 sec/100 ml, which was considered to be substantially uniform.

Among them, it was confirmed that the air permeability deviation was the smallest in the case of Example 1 with the temperature condition of 70° C.

Through the above experimental examples, it was confirmed that the electrode assembly according to the present invention had proper and uniform air permeability and adhesive force.

On the other hand, in the case of Comparative Example 1, the deviation in air permeability between each location was smaller than that of the Example, but it could be confirmed that the upper surface air permeability and the lower surface air permeability were each independently less than 80 sec/100 ml, so that safety was lower than that of the electrode assembly according to the present invention. It is believed that this is because only the primary heat press operation was performed.

In the forgoing, the present invention has been described with reference to the exemplary embodiment of the present invention, but those skilled in the art may appreciate that the present invention may be variously corrected and changed within the range without departing from the spirit and the area of the present invention described in the appending claims. 

What is claimed is:
 1. An electrode assembly, comprising: a plurality of electrodes arranged in a stack along a stacking axis, wherein each of the electrodes in the stack is separated along the stacking axis from a successive one of the electrodes in the stack by a respective planar portion of an elongated separator sheet, the elongated separator sheet being folded between each planar portion such that the elongated separator sheet follows a serpentine path traversing back and forth along an orthogonal dimension orthogonal to the stacking axis to extend between each successive one of the electrodes in the stack, wherein each of the electrodes in the stack has a first lateral end and a second lateral end on opposite sides of the respective electrode in the orthogonal dimension, and wherein the first lateral ends of a plurality of electrodes is offset by a first distance in the orthogonal dimension with respect to the first lateral end of either the first electrode in the stack or one of the two adjacent electrodes in the stack, the first distance being no more than 10% of a lateral width of any select one of the electrodes, the lateral width being defined between the first and second lateral ends of the select electrode.
 2. The electrode assembly of claim 1, wherein the first lateral end of the at least one of the plurality of electrodes is offset by the first distance in the orthogonal dimension with respect to the first lateral end of one of the two adjacent electrodes in the stack, the first distance being no more than 10% of the lateral width of the select one of the electrodes.
 3. The electrode assembly of claim 1, wherein the first lateral end of the at least one of the plurality of electrodes is offset by the first distance in the orthogonal dimension with respect to the first lateral end of the first electrode in the stack, the first distance being no more than 10% of the lateral width of the select one of the electrodes.
 4. The electrode assembly of claim 1, wherein the first distance is from 0.1 mm to 10 mm.
 5. The electrode assembly of claim 1, wherein the plurality of electrodes in the stack comprise positive electrodes and negative electrodes alternately disposed with respect to one another along the stacking axis, and wherein the lateral width of the positive electrodes is greater than the lateral width of the negative electrodes.
 6. The electrode assembly of claim 1, wherein the plurality of electrodes in the stack comprise positive electrodes and negative electrodes alternately disposed with respect to one another along the stacking axis, and wherein the lateral width of the positive electrodes is the same as the lateral width of the negative electrodes.
 7. The electrode assembly of claim 1, wherein the plurality of electrodes in the stack comprise positive electrodes and negative electrodes alternately disposed with respect to one another along the stacking axis, and wherein the lateral width of the positive electrodes is smaller than the lateral width of the negative electrodes.
 8. The electrode assembly of claim 1, wherein the plurality of electrodes in the stack comprise positive electrodes and negative electrodes alternately disposed with respect to one another along the stacking axis, and wherein the negative electrode is thermally bonded to the separator, and wherein the separator is thermally bonded to the positive electrode.
 9. The electrode assembly of claim 1, wherein the stack further includes an outer separator encircling a perimeter of the stack.
 10. The electrode assembly of claim 9, wherein the outer separator is an integral portion of the elongated separator sheet.
 11. The electrode assembly of claim 9, wherein an inner side of the outer separator is thermally bonded to at least one of a folded portion of the elongated separator or the first or second lateral ends of at least one if the electrodes in the stack.
 12. An electrode assembly comprising: a plurality of electrodes arranged in a stack along a stacking axis, wherein each of the electrodes in the stack is separated along the stacking axis from a successive one of the electrodes in the stack by a respective planar portion of an elongated separator sheet, the elongated separator being folded between each planar portion such that the elongated separator sheet follows a serpentine path traversing back and forth along an orthogonal dimension orthogonal to the stacking axis to extend between each of successive one of the electrodes in the stack, wherein each of the electrodes in the stack has a first lateral end and a second lateral end on opposite sides of the respective electrode in the orthogonal dimension, and wherein the first lateral ends of more than one of the plurality of electrodes are aligned along a line extending parallel to the stacking axis.
 13. An electrode assembly comprising: a plurality of electrodes arranged in a stack along a stacking axis, wherein each of the electrodes in the stack is separated along the stacking axis from a successive one of the electrodes in the stack by a respective planar portion of an elongated separator sheet, the elongated separator being folded between each planar portion such that the elongated separator sheet follows a serpentine path traversing back and forth along an orthogonal dimension orthogonal to the stacking axis to extend between each of successive one of the electrodes in the stack, wherein the stacking axis connects a centroid of each of multiple ones of the electrodes in the stack, and wherein a centroid of at least one of the plurality of electrodes is offset by a first distance in the orthogonal dimension with respect to the stacking axis, the first distance being no more than 10% of a lateral width of any select one of the electrodes, the lateral width being defined between first and second lateral ends of the respective electrode on opposite sides of the select electrode in the orthogonal dimension. 